Electrodeposition of Co–P Films from Alkaline Electrolytes

We study the influence of solution chemistry on the electrodeposition of Co–P from a citrate–glycinate alkaline electrolyte. The concentration of different cobalt complexes is calculated from chemical equilibria as a function of solution pH to examine the strength of the complexing agents, and compared with cyclic voltammetry (CV) data. CV and electrochemical quartz crystal microbalance are utilized to elucidate the effect of different P sources ( or ) on the electrodeposition process. The influence of plating conditions as well as different P sources on the deposit composition, microstructure, and magnetic properties are investigated. Both citrate and glycine are good complexing agents for cobalt, the former having a stronger effect. The addition of depolarizes cobalt reduction, while P codeposition from solutions containing is negligible. Pure cobalt and Co–P films grown from the source display a hexagonal close-packed (hcp) crystal structure and soft magnetic properties. The Co–P films grown from solutions containing display an amorphous structure with a P content above atom % in the deposit. Only when the plating current is small and the P content is low the films are crystalline with an hcp structure. These latter films display in-plane magnetic anisotropy and a relatively high coercivity.